Purification of phosphazene monomer

ABSTRACT

A process for increasing the yield of useful products obtained from polymerization of the distillate from impure commercially available (NPCl2)n starting material, to (NPCl2)x rubber and derivatives thereof, the process consisting of preheating the impure material prior to distillation thereof. The subscript &#39;&#39;&#39;&#39;n&#39;&#39;&#39;&#39; in this specification represents an integer generally 7 or less. The subscript &#39;&#39;&#39;&#39;x&#39;&#39;&#39;&#39; in this specification represents an integer up to about 50,000.

ited States Patent [191 1 Halasa et al. Aug. 13, B974 Audrieth et al.,Chemical Reviews, Vol. 32, Pages [75] Inventors: Adel F. Halasa, Bath;Dennis L. I 1 1422, (]943) Snyder, Kent, both of Ohio [73] Assignee: TheFirestone Tire & Rubber Primary Examiner-M. Weissman Company, Akron,Ohio [22] Filed: Dec. 3, 1971 [57] ABSTRACT [2]] Appl. No.: 204,707 Aprocess for increasing the yield of useful products obtained frompolymerization of the distillate from impure commercially available(NPCl starting mate- [52] US. Cl. 423/300, 260/2 rial, to pc y rubberand derivatives thereof, the [51] Int. Cl. C01!) 21/00, COlb 25/00process consisting of preheating the impure material [58] Fleld ofSearch 423/300 prior to distillation thereof The subscript in thisspecification represents an integer generally 7 or less. References (medThe subscript x in this specification represents an UNITED STATESPATENTS integer up to about 50,000. 3,370,020 2/1968 Allcock et al423/300 ux 3,379,510 4/!968 Jaszka 423/300 2 Clams N0 DrawmgsPURIFICATION OF PHOSPHAZENE MONOMER The classical methods for preparing(NPCl by reaction of PCl with NH CI result in a product which comprisestrimer, tetramer and higher oligomers, both cyclic and linear, e.g., asdescribed in U.S. Pat. Nos. 3,462,247 and 3,026,l74 and elsewhere in theliterature, the composition of the product varying from batch to batchdependingon variations in the purity of the starting materials and theirrelative proportions, variations in the reaction conditions, and otherfactors not fully known. 1

As a consequence, when polymerization of the impure product is attemptedto form polymers such as those described in U.S. Pat. Nos. 3,370,020 and3,515,688, the ultimate product possesses properties which are not aspredictable as would be desired.

It has now been found that the yield of useful polymer product can begreatly improved by a preliminary heat treatment of the impure materialprior to the distillation thereof. The distilled material which has beenheat-treated prior to distillation yields a high yield of useful productwhen polymerized.

Briefly, the present invention resides in the heating of impure (NPCl ina vessel adapted to be heated under a suitable atmosphere for a briefinterval of time prior to the distillation of impure (NPCl andthereafter proceeding with the polymerization procedure as described inU.S. Pat. No. 3,515,688 noted above.

Although the reason for the nature of the changes which are broughtabout by the preliminary heating are not fully understood, it is foundthat a more predictable polymerization and a higher yield of solublelinear polymer from the impure starting material results from theheating.

The procedure will be more fully understood from the example whichfollows which illustrates a preferred practice of the invention.

lmpure commercially available (NPCl is charged to a distillationapparatus open to the air. The apparatus is evacuated and filled toambient pressure with N The temperature is then raised to approximately220 C. and held at that temperature to 180 minutes.

The use of a nitrogen atmosphere is presently preferred in order toinsure greater uniformity in the products, but air, argon or other noblegases may be used in place of the nitrogen.

Similarly, a temperature in the range of 220 C. to 250 C. is preferred,but temperatures as low as 70 C. to 90 C. could conceivably be used,although the heating time would be extended to an impractical extent.

The preheating is preferably carried out at atmospheric pressure, butlower or higher pressures can be used, depending on the temperature andduration of heating.

After the preheating has been effected, and the impure (NPCl has beendistilled, polymerization'of the distillate is carried out as describedin the prior art, e.g.,

by heating in an inert atmosphere at temperatures between about 220 C.320 C., in a polymerization vessel in which the pressure is initiallyreduced to about 10' mm Hg, whereby a (NPCl rubber is produced which isreadily derivatized as described in U.S. Pat. Nos. 3,370,020, 3,515,688and elsewhere in the prior art.

The invention will become more readily apparent from a comparison ofExamples 1 and 2 which follow.

EXAMPLE I A 12 liter flask fitted with a take-off condenser (heated witha heating tape to prevent solidification of the distillate) and athermometer to measure liquid temperature was charged with 12 pounds ofimpure commercially available phosphonitrilic chloride trimer percenttrimer, 30 percent tetramer). The flask was heated with a heating mantleand distillation was started when the pot temperature reached l35l40 C.The distillate temperature was ll2-l 18 C. at 5 mm. Hg. A fraction wascollected which was percent of the impure material charged to the flask.Only 50 percent of the fraction collected gave useful (NPCl monomer forpolymerization to (NPCl rubber.

EXAMPLE [I The procedure of Example I was repeated except thedistillation vessel was preheated at 200250 C. under a nitrogenatmosphere for 2 hours. After the preheat treatment the distillationvessel temperature was adjusted to -l40 C. and the distillation wasstarted. A fraction was collected at 115 C.l22 C. which accounted for 90percent of the total charge. All of the fraction collected -was usablefor polymerization to (NPCl rubber. The chloride rubber gave usefulproduct when derivatized with fluoroalcohols by means known in the art,e.g., as described in the above noted United States patents.

We claim:

1. A process for increasing the yield of useful polymer productsobtained by the thermal polymerization of impure (NPCl produced byreaction of PCl with NH Cl wherein n represents a small integer lessthan about 7 and which impure (NPCl consists principally of (NPCl and(NPCl which process consists of:

1. preheating said impure (NPCl under an inert atmosphere for a briefinterval of time insufficient to effect any substantial polymerizationof said impure NPCl said heating being for between about 15 minutes andabout minutes and at a temperature about 220C;

2. thereafter distilling the preheated material;

3. recovering the distillate produced as a result of said distillation;and 4. then polymerizing said distillate by heating the same in an inertatmosphere at temperatures be- -tween about 220C and 320C in apolymerization vessel in which the pressure is initially reduced toabout l0- mml-lg to produce useful products of the general formula(NPCIQ wherein x represents an integer less than about 50,000.

2, The process of claim 1 wherein the preheating is under a nitrogenatmosphere.

2 3 UNITED STATES PATENT GFFICE I CERTIFICATE OF CORRECTION Patent No I5 829 Dated Aug 5 97 n n vAdel F Halasa and Dennis L. Snyder It iscertified that error appears in the above-identified patent and thatsaid Letters Pstent'ate-hereby cottecte'd as shown below:

In Column 1 Line #8, "220C." should be --2ooc.---. In Column 2, Line 44,"(NPC12),|7" should be --(1\ c1 Signed and sealed this 19th day' ofNovember 1974.

(SEAL) Attest:

c. MARSHALL DANN Commissioner of Patents MCOY M. GIBSON-- JR. AttestingOfficer

2. The process of claim 1 wherein the preheating is under a nitrogenatmosphere.
 2. thereafter distilling the preheated material; 3.recovering the distillate produced as a result of said distillation; and4. then polymerizing said distillate by heating the same in an inertatmosphere at temperatures between about 220*C and 320*C in apolymerization vessel in which the pressure is initially reduced toabout 10 3 mmHg to produce useful products of the general formula(NPCl2)x wherein x represents an integer less than about 50,000.